The
night sky in the World

Satellite
monitoring of the artificial night sky brightness and the stellar
visibility

The Night Sky in the Next Century

We are
studying the effects of the increase of light pollution which is exponential
almost everywhere with average yearly growth rates as large as 5%-10% measured
both in US and Europe. Some preliminary projections have
been tentatively made based on usual growth rates.

Growth of
light pollution in Italy 1971, 1998, 2025

.

The figure
shows the growth of light pollution in Italy. At left the map of artificial sky
brightness in 1971 (Bertiau, Treanor, De Graeve 1973); at centre our map
calibrated to 1998; at right a possible scenario of the artificial sky
brightness in 2025. We compared Bertiau’s map with a map obtained with
satellite data using the same propagation law used by them (Treanor law), we
determined the average growth from 1971 to 1998 and then we rescaled our map of
1998 to 2025 assuming the same growth.

This figure is copyright but may
be reproduced by the press in articles citing our research with the following
credit/copyright statement:

Levels correspond to a fraction of a reference natural sky brightness (251 ucd/m^2):

map 1971 (Bertiau
et al.)

Ourmap 1998, 2025

<5%

6-15%

black

grey

<11%

black

16-35%

blue

11-33%

blue

36-110%

green

33-100%

green

>1.1

yellow

1-3

yellow

3-9

orange

9-27

red

27-81

violet

>81

hot white

Yellow
indicates an artificial sky brightness equal to the natural (so the total is
double).

Orange corresponds approximately to areas where the Milky Way is very difficult
to see. At sea level, where the majority of the population lives, the Milky Way could be mostly invisible from Italy in 2025.

Red
corresponds to areas where less than a hundred of stars is visible from the zenith
to 30 degrees elevation.